Production of vitreous glazes or enamels for coating metals



Patented Nov. 24, 1953 PRODUCTION OF VITREOUS GLAZES 0B ENAMEIZS FOR COATING'METALS Reginald Percy Fraser, Surrey, and Alfredo Luigi Cianclii', Hampstead, London, England No Drawing. Application Maylfi liiefl, Serial No. 93,639

Claims priority, application Great Britain June 1, 194:8

7 Claims. 1.

This inventionrelates to the vitreous glazing or' vitreous enamellin'g of the surface of aluminium and aluminium base alloys and articles thereof.

Glazes and vitreous enamels suitable for application to aluminium have hitherto been prepared containing high percentages of lead oxide in order to attain the required low fusion or maturing temperature.

There are certain trade restrictions that render the manufacture and use of vitreous enamelling: compositions containing lead objectionable. One of the objects, therefore, of the present invention is to provide an improved lead-free vitreous enamel composition suitable for the? surface? finishing of aluminium and its alloys.

Owing to the low melting pointv of aluminium and its alloys as compared with iron or steel, the vitreous enamel compositions available and commonly used for the enamelling of. iron by the usual stoving or furnace treatment at temperatures from 800 C. to 1100 C. cannot be used for enamelling aluminium or its alloys by stoving or furnace treatment. A further. ohi ject of' the present invention is, therefore, to provide a lead-free vitreous enamelling composition having a fusion or maturing temperature below 600 C.

Owing. to thehigh co-efliicent or thermal ex pension of aluminium and its alloys, as compared with steel or glassware and ceramic ware, a still further object. of the invention is to provide a lead-free enamelling composition for aluminium and its alloys which has a thermal co-efti'ci'ent of expansion approximately the same as that of the aluminium or alloy thereof to be enamelled, as otherwise the enamel will flake" off or distor' the enamelled article.

Owing to the ductility and softness of aluminium compared with steel or ceramic bodies, a still further object of the invention is to providealead-free enamelling' composition for aluminium and its alloys which becomes chemically bonded to the alumim'um during the stoving treatment, preferably without special pretreatment of the aluminium surface, so that bending ordenting of the aluminium does not throw off the enamel.

Owing to the exceptionally low softening point required in an enamel for aluminium; a still further object of. the invention is to provide a lead-free enamelling composition for aluminium and its alloys which retains a high degree of surface hardness to prevent abrasion and also a high. degree of chemical. resistance against water, dilutev acids, and alkalies;

Ceramic. glazes and enamels for. iron and steel and ceramic ware usually have, calculated as: male percentages,

ratios varying from 1.5 to as high as 12.0 with maturing'temperatures ranging from 700 C. to 120.0" C. where. R20 stands for the oxides of the elements Li, Na and/or K (of group I of the periodic table); RO= stands for the oxides of the elements Mg, Ca, Zn, Sr and/or Ba (of group II); R203 stands for the oxides of the elements B and/or A1 (of group III) and R02 stands for the oxides of the elements Si, Ti, Zr and/or Sn (of group IV).

It has previously been thought that ceramic glazes and enamels even without lead having a ratio below 1.5 are commercially useless, having far too high a solubility; nevertheless our novel compositions have be arranged in the following. groups of oxides:

R20, 13-24%; RO, 6'20%;

It will be noticed that such compositions are characteriscclby an exceptionally high percent ago of the group of oxides R201, this group consisting of aluminium oxide, which ranges from 12 to 17%, and horic oxide which ranges from 25 to 40%, and that the ratio ranges from 2-2- to =1.2 to 4.3

In contrast with such compositions it is important to note that because the thermal coeflicient of expansion of aluminium and its alloys is much higher than that of glass or ceramic materials, our glazing compositions do not contain more than a moderate percentage of borio oxide, which has a very low co-efiicient of expansion. Moreover, in the case of applying vit= reous enamelling compositions to the surface of aluminium or its alloys, the ideal bonding to the metal or alloy by the glazing composition is one which establishes a chemical combination with the oxide film on the aluminium surface or a gradation of aluminium content from a maximum in the metal to a minimum in the glaze. Therefore, our vitreous enamelling com position for application to aluminium or its alloys does not of itself contain a high percentage of aluminium oxide because at the interface the aluminium oxide itself is present and will tend to increase the aluminium content in the interface of the applied composition and establish the bond referred to.

The co-eflicient of thermal expansion of aluminium and its alloys in the temperature range 10-100 C. lies between 20.0 10 and 24.0 10- whereas steel in the same temperature range has a co-eflicient of 10.0 l Lead-free glazes and enamels have hitherto been prepared having, in the same temperature range, co-efficients up to 123x10 Enamels according to this invention should, therefore, have co-efiicients of thermal expansion greater than 15.0 between l0-100 0.

According to the present invention we provide lead-free vitreous enamelling compositions suit- 4 line earth oxides and a comparatively low con tent of B203 with or without a low content of A1203.

Expressed as mole percentages the main con- 5 stituents of our new glazing compositions are characterised by a combination of the groups of oxides as follows:

of which 13-36% is 3102.

Thus, the ratio SiO i-R O 26 to 53 9 L uQ The main constituents of our novel glazing compositions can be expressed as mole percentages within the following ranges:

TABLE I Sodium oxide and potassium oxide with or without lithium oxide 21 to 36% R10 Barium oxide with or without calcium oxide or strontium oxide or ziic oxide 17 to 30% R0 Boric oxide, 8 to 13%} 8 to Paco Aluminium oxide, 0 to 4% m Silica l8to SiOz (R02) It will be observed that not only is there an absence of lead in the composition but that the proportion of boric oxide does not exceed 13 mole percent and the proportion of aluminium oxide does not exceed 4 mole percent, whilst the R203 content does not exceed 17%. On the other hand, the alkali oxide and alkali earth oxide percentages are high.

n To the above composition may be added one 05 or more of the following opacifiers:

giitauium oxide ('lflg) 0 to 15? r omum xid I. Tin oxidc SnO2) 2 I: to 15% R02 raising the possible R02 content of the glazes that are opacified up to 51 The following is a weight percentage table of dry-batch components for treatment to make frits which produce enamels as above specified:

TABLE 2 Percent dry batch compositions 1 l 2 i 3 4 5 6 7 8 I 9 I 10 11 12 Lith. carb., LizCOa 5. 5.8 6-3 5.6 7.8 8.6 8. 6 9 0 6.4 Sod. ash, NazCOs 5. 8 5. 2 5. 0 5. 9 7. 5 7. 9 a. 7 a. 1 8.9 "ibj 1: Pot. carb. (anhydrous), KzCOa 3.8 7.2 6.6 6.0 4 3 6.6 7.1 10. 9 11.4 10. 6 15. =3 Stront. carb., SrCOa -8 3. 5 Cale. oath, CaCOa. 6.7 10.8 11.4 16.7 10.0 17 7 13.0 Barium 02th., B4003. 25. 0 24. 9 28. 8 l9. 0 1S. 7 17. 8 13. 0 13. Zinc oxide, Z110 Borax, N21 B O7.10H O 15. 7 0 20. 2 20. 0 l9. 3 21. 8 2L 6 Silica, SiOg i 0 5-0 9- 1 7. l 8. 6 8.5 9.1 Felspar, K:O.A1zO s.6S10z 13.2 10. 9 10. 5 12. 4 10. 9 10. 9 11. 1 Titanium (1i0X., T102 6. 2 6. 1 1.1 5. 6 9. 9 6. 2 6. 0 Zirconium oxide Zl'Oz 1.0 l. l 1.0 l. 7 1,0 1.0 1.5 Tin oxide, S1102 4. 7 0 0 2. 3

able for bonding to the surface of aluminium m an below 1.5.

More particularly the lead-free low-melting glazing compositions according to our invention The ingredients used in making up a batch composition may take the form of oxides, carbonates, nitrates or silicates. In the case of alumina, at least some of it is preferably taken in the form of potash felspar.

To prepare any selected composition the component materials (other than any desired colouring oxides) are mixed together and then heated and melted and fritted in water and then ground and pulverised. During the grinding process traces of colouring oxides or opacifiers may be added for colouring the eventual glaze.

The resulting frits expressed as a combination of oxides in percentages by weight will be contain high contents of alkali oxides and alkarespectively as follows:

TABLE 3 Frit compositions-percentage oxides l 2 3 4 5 6 7 8 9 10 ll 12 11.316 10.46 11.63 9.30 9.98 11.25 11.10 10 61 10.96 11.30 10 U3 2. 96 2. 88 2. 42 3.02 2. 98 3. 0O 3. 06 3 51 v 3. 76 4. 24 3 98 8. 52 1. 61 3.26 7. 2D 13. 88 8. 66 1. 5S 1. 48 1. 63 2. 16 1. 41 1. 44: 2. 82 4. 34 Total 1301...- 41. 31 30. 97 I 37 32 27.70 23 42 27 13 27. 31, 234237,

The fusion temperatures of these frit compositions range from 500 C. to 600 C. The compositions Nos. 9, 10, 11 and 12 are for clear glazes.

The twelve compositions listed in Tables 2 and 3 but expressed as mole percentages (falling within the ranges of Table I) are represented as follows:

combine chemically with it, so as to produce a resistant matt finish.

Some operating details of interest in carrying out the invention are as follows:

The articles to be enamelled are preferably cleaned, either chemically as with an alkali wash or by treatment with a degreasing liquid, or mechanically as by sand-blasting or thermioally as TABLE 4 Fn't compositionsmolecular percent amides TQLaIPiO ZrO SnO 12.0 9.2 25 4.2 7 15.0104 101 1.3 1.3 1.3 ,1

ex-11w. 00.9 45.5 4.4 43.1 53.7 51.3 30.2 50.7 43.3 43.2 43.3 47,5 2 120, 43.1 04.5 51.0 50.9 40.3 43.2 40.3 49.3 30.3 30.3 30.2 32.5

When using any selected frit for application to an article to be glazed, the powdered frit is brought to the fluid state by addition of water or other liquid vehicle to form a slip which is then applied to the article, whereupon the latter is stoved below 600 C.

It will be understood that when preparing the slip a mixture of two of our frits may be used. For example, one having the lowest softening temperature with one having a higher temperature or different colour. Alternatively a ground frit may be mixed with a proportion of powdered silica or the like which at the stoving temperature will become bonded into the glaze but not by heating in a furnace chamber.

In the case of applying a glaze by stoving, the application of a first coating of the slip followed by a single stoving treatment usually results in a plain or mottled grey appearance, the actual glaze or gloss being satisfactory but a desired colour being probably imperfect because of the influence of the chemical bonding to the foundation metal. However, if the colour is as desired but a matt or egg-shell surface finish is required, this may be obtained by a second stoving treatment without any precoating with further slip. If, on the other hand, it is desired to preserve the glaze and attain the lowed by a second stoving treatment may be carried out.

If both glaze and colour are desired, coupled with a mottled or submerged crack effect, a second application of slip (either of the same colour as the first or different therefrom) followed by a quick drying, to produce a multitudinous cracking of the biscuit, followed by a rapid stoving treatment may be performed.

What we now claim is:

1. A lead-free and fluorine-free vitreous enameling composition suitable for bonding to the surface of aluminum and aluminum base alloys, said composition having a fusion or maturing temperature below 600 C. and a coefli cient of thermal expansion greater than constituents calculated asm'ole percentages;

where R20 represents oxides selected from the group consisting of the oxides of the elements Li, Na and K, R0 represents oxides selected from the group consisting of oxides of the elements Ca, Sr and Ba, R02 represents opaciiierqxi-des selected from the group consisting of the oxides of Ti, Zr and Sn, R203 represents oxides selected from the group consisting of the oxides of the elements B and Al.

2. A composition as in claim 1 wherein R0 is CaO.

3. A composition as in claim 1 wherein R0 is BaO.

4. A 1ead-free, fluorine-free, vitreous enameling composition suitable for bonding to the surface of aluminum and aluminum base alloys said composition having a fusion or maturing temperature below 600 C. and a ooeflicient of thermal expansion greater than 15.0 l0 in the temperature range 10-100 C., said compo sition consisting essentiallyof the constituents said composition having a fusion or maturing temperaturebelow 600". C. and a coeflicient of thermal expansion greater than 15.0 10 in the temperature range 10-l00' C. said composition consisting essentially of the constituents calculated as'mole percentages in the following ranges:

R20, 21 to 36% R0, 17 to 30% B203, 8 to 13% A1203, up to 4% S102, 18 to 36% where R20 represents oxides selected from the group consisting of the oxides of the elements Li, Na and K, and R0 represents Oxides select ed from the group consisting of oxides of the elements Ca, 'Sr and Ba.

6. A lead-free, fluorine-free, vitreous enameling composition suitable for bonding to the surface of aluminum and aluminum base alloys 53 said composition having a fusion or maturing temperature below 600 C. and a coeflicient of thermal expansion greater than 15.0 10- in calculated as mole percentages in the following 1 ranges:

R20, 21 to 36% R0, 17 to 30% B203, 8 13% SiOz, 18 to 36% where R20 represents oxides selected from the group consisting of the oxides of the elements Li, Na and K, and R0 represents oxides selected from the group consisting of oxides of the elements Ca, Sr and Ba.

5. A lead-free, fluorine-free vitreous enameling composition suitable for bonding to the surface of aluminum and aluminum base alloys the temperature range 10100 0., said composition consisting essentially of the constituents calculated as mole percentages in the following ranges:

R20, 21 to 36% R0, 17 to 30% B 03, 8 to 13% A1203, up to 4% Si02, 18 to 36% 'I'iOz, up to 15% ZrOz, up to 5% SnOz, up to 5% where Ti02+Zr02+Sn02 does not exceed 15%, and where R20 represents oxides selected from the group consisting of the oxides of the elements Li, Na and K, and R0 represents oxides selected from the group consisting of oxides of the elements Ca, Sr and Ba.

7. A composition as in claim 1 wherein R0 is a mixture of BaO and C210.

REGINALD PERCY FRASER. AFREDO LUIGI CIANCHI.

References Cited in the file of this patent UNITED STATES PATENTS Number 7 Name Date 1,833,087 Migeot Nov. 24, 1931 1,944,938 Kinzie Jan. 30, 1934 2,414,633 Bryant Jan. 21, 1947 FOREIGN PATENTS Number Country Date 156,822 Austria 1939 610,645 France 1926 868,052 France 1941 602,244 Germany 1934 

1. A LEAD-FREE AND FLUORINE-FREE VITREOUS ENAMELING COMPOSITION SUITABLE FOR BONDING TO THE SURFACE OF ALUMINUM AND ALUMINUM BASE ALLOYS, SAID COMPOSITION HAVING A FUSION OF MATURING TEMPERATURE BELOW 600* C. AND A COEFFICIENT OF THERMAL EXPANSION GREATER THAN 15.0X10-6 